In xerography (also known as electrophotography, electrostatographic printing, and colloquially as “photocopying” and “laser printing”), an important process step is known as “fusing.” In the fusing step, a dry marking material, such as toner, is placed in imagewise fashion on an imaging substrate, such as a sheet of paper. The toner is then subjected to heat and/or pressure in order to melt or otherwise fuse the toner permanently on the substrate. In this way, durable, non-smudging images are rendered on the substrates.
Currently, the most common type of fusing apparatus (“fuser”) used in commercial xerographic printers includes two rollers, one typically called a “fuser roll,” and the other a “pressure roll.” The two rolls are arranged adjacent to one another and in contact, thereby forming a nip for the passage of the substrate therethrough. Typically, the fuser roll is hollow and further includes one or more heating elements in its interior. The heating elements are adapted to radiate heat in response to a current being passed therethrough. The heat from the heating elements passes through the surface of the fuser roll, which in turn contacts the side of the substrate having the image to be fused. The combination of heat and pressure is applied to the entire page, thereby successfully fusing the image.
Unfortunately, present-day fusers tend to be one of the most expensive subsystems within a xerographic printer, and can often suffer from reliability issues. Accordingly, alternative approaches for fusers have been developed. For example, U.S. Pat. No. 5,459,561 to Ingram, entitled “Method and apparatus for fusing toner into a printed medium” (hereinafter, “the '561 patent”) discloses a method for fusing toner into a printed medium by projecting a high-energy laser beam onto a toner image using an optical scanner. The laser radiation serves to heat the developed toner image on the printed medium. The high-energy laser beam is synchronized with a low-energy laser beam, which is used to develop the latent image on the photoconductive drum or belt. Unfortunately, the approach of the '561 patent is rather complex and expensive, and is not particularly efficient.
Other approaches for fusing are set forth in U.S. Pat. No. 5,436,710 to Uchiyama, entitled “Fixing device with condensed LED light” (hereinafter, the '710 patent). The '710 patent discloses a fixing device for fixing toner images onto a sheet, wherein the device includes a light-emitting diode (LED) array and a cylindrical lens. The cylindrical lens is arranged to condense the light from the LED array onto the surface of the sheet, thereby fixing the toner to the sheet. The various fusing approaches set forth in the '710 patent all involve heating the entire sheet by uniform activation of the elements in the LED array. Thus, the approaches set for the in the '710 patent are not significantly different from other prior art methods in that they involve fusing an entire sheet, regardless of the toner image formed thereon.